A projectile of mass 0.550 kg is shot straight up with an initial speed of 22.0 m/s.
(a) How high would it go if there were no air friction?
I get 24.7m for this.

(b)If the projectile rises to a maximum height of only 13.6 m, determine the magnitude of the average force due to air resistance.
forceresistance*13.6=.5mv^2 is the formula I think I am supposed to use. I end up with 9.78. However this is wrong. What am I doing wrong?